The present invention relates to a dual-circuit pressure control valve having a change-over point determined from the outside by a control force for use in hydraulic dual-circuit brake systems of automotive vehicles. The pressure control valve includes two cylinders each connected to a different one of the two brake circuits arranged parallel to each other and housing therein the control pistons whose actuating tappets project outwardly on the same end face of the cylinder housing and abut a common yoke which is acted upon by the control force from the opposite side.
In a known dual-circuit pressure control valve (U.K. Pat. No. 2,008,216A) the two control pistons are acted upon by the pressure of two separate rear-wheel brake circuits. As soon as the pressure exceeds a predetermined value (change-over point), the two control pistons are moved in opposition to the control force which is preferably generated by a helical spring, thereby causing closure of a valve which is located between the master brake cylinder and the wheel cylinders. In this way, the pressure in the rear-wheel brake cylinders rises more slowly beginning at the change-over point than in the master brake cylinder.
The disadvantage of the known dual-circuit pressure control valves is that the valve closure travels up to exceeding the change-over point are comparatively long so that a comparatively large amount of fluid volume is input to the control valve for actuating the control pistons.